The present invention relates to a and to an apparatus for damping vibration of an m-phase alternating-current motor.
The moment of an AC machine is generated by the voltage supplied to the armature circuit, normally a stator, and magnetisation of the excitation circuit, normally a rotor. The supply voltage is fed into the stator windings, which are fitted in slots in the stator. Magnetisation is developed by means of permanent magnets or excitation windings fitted in the rotor. The smoothness of motor operation depends on how closely the magnetic field developed in the air gap of the motor approaches the sinusoidal form. The harmonic components of a non-sinusoidal curve form produce moments that result in mechanical vibration and noise, the frequency of such moments depending on the frequency of said components.
Besides being dependent on the frequency of the supply voltage, the form of the air gap field also depends on the form of the field produced by excitation, among other things. Moreover, in machines with a small number of slots per phase and field pole, the so-called slot-harmonic field produced by the current flowing in each slot is stronger. For example, in a three-phase machine with one slot per phase, the six-fold supply frequency is a problem.